1. Field of the Invention
The present invention relates to an image forming method and an image forming apparatus, and more particularly to a toner image transfer type electrophotographic image forming method and an apparatus adopting the method.
2. Description of Related Art
In the art of electrophotography, a method of reproducing a full color image having the following processes is well-known. First, an original full color image is color-separated into images of three primary colors. Next, an electrostatic latent image corresponding to each of the three Primary color images is formed on a photosensitive member (electrostatic latent image carrying member), and the latent image is developed into a toner image thereon. Then, the toner image is transferred to a transfer medium (first transfer). The processes from the electrostatic latent image formation through the first image transfer are repeated until all the three primary color images are overlaid on the transfer medium. Thereafter the overlaid toner images are transferred to a copy sheet (second transfer). However, in a conventional full color copying apparatus adopting this method, charge applied to a toner image for the first transfer of the toner image is left thereon, and this negatively influences the first transfer of a next toner image.
In the light of this problem, Japanese Patent Laid Open Publication No. 62-36220 proposes that charge on a toner image is reduced immediately after the transfer of the toner image to the transfer medium.
The toner image charge erasure is effective on the first image transfer. However, problems caused by poor second image transfer, such as density unevenness and white spots appearing on the reproduced image on the copy sheet, and problems caused by reversion of toner from the transfer medium to the photosensitive member during the first transfer of successive toner images, such as an increase of the amount of residual toner and color imbalance of the copy image, are left unsolved. In this specification, density unevenness and white spots appearing on a copy image are referred to as image noise.